The present embodiments relate to a computed tomography (“CT”) device having transformer-type transmitters for the contactless transmission of electric power in the sense of a transfer of energy from a stationary part to components of a rotating part.
X-ray CT is an x-ray recording method, which has a different image structure than the conventional x-ray layer recording method. In the case of CT recordings, transverse sectional images are obtained, such as images of body layers. The images of body layers are oriented perpendicular to the axis of the body. The tissue-specific physical variable shown in the image is the distribution of the attenuation value of x-ray radiation μ(x,y) in the sectional plane. The CT image is obtained by reconstructing the one-dimensional projections of the two-dimensional distribution of μ(x,y) provided by the measuring system used from numerous different viewing angles.
The projections originating from different directions, such as at a projection angle α, are obtained using a combined x-ray tube-detector system. The x-ray tube-detector rotates in the plane of the layer about the object. The x-ray tube-detector may include “fan beam devices” having a tube and an array of detectors (a linear or partially circular arrangement of detectors) rotating in the plane of the layer in a common manner about a center of rotation. The center of rotation is also the center of the circular measurement field.
FIG. 1 shows a schematic diagram of a CT device for a fan beam method. The CT device comprises a rotatable support 3 in a frame 2. The rotatable support 3 is able to be rotated by a motor 4 about an axis 5 running perpendicular to the plane of the drawing.
An x-ray tube 7 and a detector 8 for x-ray radiation are provided to scan the patient 1 lying on a support 6. The x-ray tube 7 emits a fan-shaped x-ray radiation beam 9. The entire transverse layer of the patient 1 to be examined is penetrated by x-ray radiation beam 9. The thickness of the x-ray radiation beam 9 perpendicular to the plane of the layer is equal to the thickness of the layer, for example, a few millimeters.
In order to scan the patient 1, the measuring arrangement, which includes x-ray tube 7 and detector 8, is rotated 360° about the patient 1 and a set of output signals of the detector 8 is read at predetermined projections (e.g. Δα=1°).
The detector 8 includes a series of single detectors, for example, 256 single detectors, so that α, for example, 256, signals of the detector 8 are read (detected) per projection. For example, 360×256 signals are available for processing per scanning procedure. The signals are transmitted to a fixed (stationary) data processing facility. The data processing facility calculates the attenuation values μ(x,y) of predetermined points in the examined transverse layer of the patient 1 in the form of a matrix. The data processing facility effects a pixel-based image reproduction on a screen 11.
FIG. 1 shows an exemplary embodiment of a double contactless, inductive energy transmission from the stationary part to the x-ray tube 7 and to the detector 8 by transmitters 21, 22. The transmitters 21, 22 respectively form a transformer. The transmitters 21, 22 are configured as concentric rings and enclose the opening 23. The opening 23 receives the patient 1.
FIG. 2a shows a cross section of the two annular transmitters 21, 22. Typically, each transmitter 21, 22 has a primary winding and a secondary winding, which are surrounded by a transmitter core.
The transmitter core of the outer transmitter 21 is a pot-type core enclosing the primary winding 24 and the secondary winding 26. The outer transmitter 21 includes two core parts 25, 27 of U-shaped cross section. The two core parts 25, 27 are oriented with their flange-type shoulders facing each other. The core part 27 and the secondary winding 26 of the first (outer) transmitter 21 or, respectively, the core part 31 and the secondary part 30 of the second (inner) transmitter 22 are fixed in relation to the rotatable support 3 and the x-ray tube 7 and detector 8, and rotate with the measuring arrangement 7, 8. The other core part 25 and the primary winding 24 of the outer transmitter 21 or, respectively, the other core part 29 and the primary winding 28 of the inner transmitter 22 are provided in a fixed manner in the device. An air gap 19 is left between the two core parts 25, 27 or, respectively, 29, 31.
The electric power required can be transmitted in an inductive and contactless manner to the rotating part of the gantry (scanning unit comprising x-ray source 7, detector 8 with electronic measuring system and mechanical structure, e.g. rotatable support 3). The power consumption of the x-rays tube at approx. 80 kWatt is significantly higher than the power consumption of all further components of the rotating part of the gantry (rotary anode, detector, electronic measuring system, heating unit for the x-ray tube, etc.), which is around 10 kWatt in total. The electrical supply is divided into two separate load circuits and use two separate transmitters 21, 22. Separation of the two supply units allows optimum design of both load circuits.
An inductive and contactless transmission of electric power does not use energy transmission by way of slip rings. The inductive and contactless transmission of electric power avoids, for example, sparking, loss of contact and premature wear. The transfer of measurement data uses a contactless transmission, for example, optically or by way of a high-frequency transmission system, with modern CT systems.
FIG. 1 shows an optical transmission system for contactless transmission of detector signals. A ring 12 is made of light-conducting material (e.g. plexiglass) and curved around the axis of rotation 5. The ring 12 is irradiated at one point by way of an optical system 14 using a light source 13. The light source 13 is connected to a modulation stage 15, which converts the detector signals to light signals. The ring 12 is configured in such a manner that the light from the light source 13 is routed over the entire ring 12 periphery. The ring 12 has a gap 16 and a light detector 17, which converts the light signals back to electrical signals. The light detector 17 is disposed on one of the faces bordering the gap 16. The light signals are demodulated in a demodulation stage 18 and are supplied to the data processing facility 10. Signal transmission takes place during a projection in a consecutive manner. The detector signals of the individual detector elements are transmitted consecutively by the described facility.
The light source 13 can, for example, be a luminescence or laser diode operating in the infrared range. The modulation stage 15, the light source 13, and the optical system 14 rotate with the rotating part of the gantry (x-ray tube 7, detector 8, etc.) while the patient 1 is being scanned. The ring 12, the light detector 17, the demodulation stage 18, and the data processing facility 10 with the screen 11 are stationary. Such an optical (data) transmission system is very complex and cost-intensive because of the large number and complexity of the components.
To summarize, an immense transfer of energy takes place between the stationary part and the rotating part of the gantry of a CT device. An intensive data exchange takes place, with both control signal data for process control and measurement data obtained using detectors and electronic measuring systems. While the transfer of the control signal data between the rotating and stationary parts takes place in a bi-directional manner, the measurement data for obtaining and processing the images has to be transmitted unilaterally to the stationary part. Conventionally, this data transfer took place by way of slip rings and/or on fiber-optical transmission paths.